Modesetting: Remove the 8k limit for the maximum resolution, and add Tear-free support

Hi everyone,

I have been working on removing the 8k-limit from the modesetting driver on Intel. This allows our users to have up to four 8k screens in a row (although the bug I initially set out to fix was for 3x4k). This turned out to become useless for Intel as Ville Syrjälä bumped the maximum stride to 32k, but this feature is still beneficial for simpler drivers.

Since my solution was introducing per-CRTC shadow framebuffers, I decided to make it worth my while on Intel platforms by adding support for another long-wanted feature: TearFree.

In an effort to test all this new code and its different codepath, I also added support to disable atomic modesetting support.

I tested the different scenarios and always got the right image, and acceptable performance (there is always room for improvement though).

Looking forward to checking out your reviews and testing results.